Large-Area, Flexible, Lead-Free Sn-Perovskite Solar Modules

For the first time, large-area, flexible organic–inorganic tin perovskite solar modules are fabricated by means of an industry-compatible and scalable blade-coating technique. An 8-cell interconnected mini module with dimensions of 25 cm2 (active area = 8 × 1.5 cm2) reached 5.7% power conversion efficiency under 1000 W/m2 (AM 1.5G) and 9.4% under 2000 lx (white-LED).


Butylammonium acetate (BAAc) synthesis
Acetic acid and butylamine were mixed in a molar ratio of 1:1.First, butylamine was put into stirring in a round bottom flask in an ice bath, and then a diluted solution of acetic acid in ethanol (1:1, v/v) was dropwise added to the flask under vigorous stirring.After the addition of acetic acid, the reaction was left in the ice bath and continuous steering for 2 hours.After that, the mixture was rotary evaporated at 60 °C for 1 h.The resultant liquid product was put into a fridge for 2 hours to crystallize, and then washed with diethyl ether and recrystallized three to five times.The resultant product was dissolved in absolute ethanol and was rotary evaporated at 60 °C for 1 h.Finally, it was cooled down to room temperature to obtain the final liquid product of BAAc.

Nickel oxide dispersion preparation
Nickel oxide nanoparticles were prepared from a 5 mol L -1 aqueous solution of nickel(II) nitrate hexahydrate, tetramethylammonium hydroxide was added to achieve a pH of 10; the precipitated Ni(OH)2 was washed with deionized water five times, then dried at 80 °C and calcinated at 270 °C for 2 h, after which a black fine powder was collected.The suspension was prepared with nanoparticles concentration of 20 mg mL -1 in a H2O:EtOH (85:15 v/v%) mixture.

Module fabrication
ITO-coated PET sheets were patterned using a near-infrared laser (1064 nm wavelength), followed by a washing process with isopropanol.Then, the sheets were dried with N2 flow and subsequently introduced in an oxygen-plasma chamber for 3 min.The PEDOT:PSS dispersion diluted in ethanol (6:1, v/v), nickel oxide dispersion, or PEDOT:complex dispersion was filtered with a 0.45 µm filter.Then, every dispersion were deposited through a blade-coating technique using an effective gap of 125 µm at a velocity of 2.5 mm .s -1 for PEDOT:PSS and nickel oxide dispersions and at a velocity of 5 mm .s -1 for the PEDOT:complex dispersion.The obtained films were annealed at 100 °C for 30 min.Additionally, for PEDOT:complex layer a Al2O3 wetting layer was deposited using 1 wt% Al2O3 dispersion in isopropanol, 250 µm effective gap and 5 mm .s -1 velocity.The perovskite deposition was done in N2 filled glovebox by blade-coating with an effective gap of 150 µm and a velocity of 0.7 mm .s -1 .During the coating, the film was dried with a nitrogen flow through an air knife.Then, the sheets were annealed at 80 ºC for 10 minutes and at 100 ºC for 20 min.A 30 nm layer of C60 was thermally evaporated on top of the perovskite layer as the electron transport layer, followed by 5 nm of BCP as a buffer layer.All layers except ITO were patterned (P2) in an ambient atmosphere (~30 min exposure) for the interconnection between cells.Then, 100 nm of Ag was deposited through a shadow mask to obtain the electrical insulation between electrodes of adjacent cells.

Scanning electron microscopy
Top-view morphology images of samples were obtained with a field emission SEM (Phenom ProX), which had an accelerating voltage of 10 kV.X-ray diffraction measurements X-ray diffraction (XRD) patterns were collected with Rigaku MiniFlex600 (Cu Kα radiation, λ=1.5406Å) diffractometer.
Current-voltage measurements J-V measurements were carried out by a Keithley 2461 source measure unit.The solar cells were illuminated with a simulated AM1.5G irradiation of 100 mW/cm 2 using an AAA-rated solar simulator obtained from Abet Technologies, sun 2000, which was calibrated against an RR-208-KG5 silicon reference cell also procured from Abet Technologies.Measurements in low-light conditions were performed under a warm white LED (CLU028-1201C4-303H7M5-F1, Citizen Electronics, ~3280 K).The spectrum of 1000 and 2000 lx illuminance was measured with the spectrometer SEKONIC C-800 Spectromaster and then, proper irradiance was calculated.

Absorption and photoluminescence measurements
Absorption spectra, and steady-state photoluminescence measurements were performed with the Edinburgh Instruments FS5 Spectrofluorometer.Samples were excited with a 405 nm laser diode.

Figure S1 .Figure S2 .
Figure S1.J-V parameters of solar modules fabricated on PEDOT:PSS for different laser operating currents.
Figure S4.J-V parameters of solar modules fabricated on PEDOT/Al2O3 for different laser operating currents.

Figure S5 .
Figure S5.Forward and reverse J-V scan for the champion module.

Figure S6 .
Figure S6.Shelf-stability of modules fabricated on PEDOT/Al2O3 for different laser operating currents.

Figure S7 .
Figure S7.Stabilized power output at maximum power point for the champion module after 3300 hours of storage time (3.94%PCE from J-V scan).

Figure S8 .
Figure S8.The experimental setup for J-V measurements in low illuminance conditions.

Table S2 .
Laser power versus output power dependence.